Hypersaturation index

ABSTRACT

Embodiments of the present disclosure provide a hypersaturation index for measuring a patient&#39;s absorption of oxygen in the blood stream after a patient has reached 100% oxygen saturation. This hypersaturation index provides an indication of the partial pressure of oxygen of a patient. In an embodiment of the present invention, a hypersaturation index is calculated based on the absorption ratio of two different wavelengths of energy at a measuring site. In an embodiment of the invention, a maximum hypersaturation index threshold is determined such that an alarm is triggered when the hypersaturation index reaches or exceeds the threshold. In another embodiment, an alarm is triggered when the hypersaturation index reaches or falls below its starting point when it was first calculated.

PRIORITY CLAIM TO RELATED PROVISIONAL APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/705,761, filed Sep. 15, 2017, entitled “Hypersaturation Index,” whichis a continuation of U.S. application Ser. No. 14/852,356, filed Sep.11, 2015, entitled “Hypersaturation Index,” which is a continuation ofU.S. application Ser. No. 13/865,081, filed Apr. 17, 2013, entitled“Hypersaturation Index,” now U.S. Pat. No. 9,131,881, which claimspriority benefit under 35 U.S.C. § 119(e) of U.S. ProvisionalApplication Ser. No. 61/719,866, filed Oct. 29, 2012, entitled“Noninvasive Partial Pressure of Oxygen Sensing System,” U.S.Provisional Application Ser. No. 61/703,087, filed Sep. 19, 2012,entitled “Noninvasive Partial Pressure of Oxygen Sensing System,” andU.S. Provisional Application Ser. No. 61/625,599, filed Apr. 17, 2012,entitled “Noninvasive Partial Pressure of Oxygen Sensing System,” thedisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the field of noninvasive oxygendelivery measurement using optical based sensors.

BACKGROUND

The measurement of oxygen delivery to the body and the correspondingoxygen consumption by its organs and tissues is vitally important tomedical practitioners in the diagnosis and treatment of various medicalconditions. Oxygen delivery is useful, for example, during certainmedical procedures, where artificially providing additional oxygen tothe patient's blood stream may become necessary. For example, during anintubation procedure, the patient will stop breathing while theprocedure is performed. The patient is typically provided with oxygenbefore the intubation procedure. Because the patient stops breathingduring an intubation procedure, the patient's blood oxygen saturationlevel will fall. In that situation, the medical practitioner must ensurethat the patient has sufficient reserves of oxygen in their systembefore intubation so that during the intubation procedure suffocation isavoided. At the same time, providing oxygen at a high pressure to apatient can cause damage to the alveoli of an adult patient. On theother hand, even normal oxygen levels can or cause blindness in neonatalpatients.

The current standard of care is to measure oxygen delivery through theuse of a pulse oximeter. Pulse oximeters measure oxygen saturation(SpO₂). SpO₂ represents the percent of available hemoglobin that canchemically bind with oxygen molecules.

Another indicator of oxygen delivery is the partial pressure of oxygen(PaO₂), However, there are currently no reliable ways to measure PaO₂noninvasively. Invasive PaO₂ measurements require expensive sensors andare known to carry serious side effects that can harm the health of apatient.

SUMMARY

Embodiments of the present disclosure provide a hypersaturation indexfor measuring a patient's absorption of oxygen in the blood stream aftera patient has reached 100% oxygen saturation. This hypersaturation indexprovides an indication of an increased level of dissolved oxygen in theplasma. This is useful, for example, for patients that are onsupplemental oxygen therapy or are on a ventilator or closed-looppositive pressure delivery device. An excessively high level of PaO₂ canbe dangerous for most patients. In some patients, for example neonates,a high level of PaO₂ can cause loss of eyesight. Significant damage canoccur to the lungs, and in particular, to the alveoli structures in thelungs, if the PaO₂ level is too high.

In another embodiment, a timer is provided that indicates when ahypersaturated patient is likely to return to a baseline saturationlevel after oxygen administration is stopped. This is useful, forexample, during an intubation procedure.

Pulse oximetry is a noninvasive technique which allows the continuous invivo measurement of arterial oxygen saturation and pulse rate inconjunction with generation of a photoplethsymograph waveform.Measurements rely on sensors which are typically placed on the fingertipof an adult or the foot of an infant. As explained in detail below, theratio of red and infrared light signals absorbed at the measuring siteis calculated (R/IR ratio). Oxygen saturation level is determined usinga lookup table that is based on empirical formulas that convert theratio of red and infrared absorption rates to a SpO₂ value.

A correlation exists between the R/IR ratio and the level of PaO₂. Thisrelationship between R/IR ratio and PaO₂ levels, however, varies frompatient to patient. For example, at the same PaO₂ level, one patient mayhave a R/IR ratio of 0.55 and another patient may have a reading of0.45. Therefore, once the absorption level reaches 100%, it becomesdifficult for the medical practitioner to assess the patient's conditionwith respect to PaO₂ and the potential dangers of a high level of PaO₂.Without the ability to accurately measure the PaO₂ level, medicalpractitioners are in need of a noninvasive way to monitor a patient'shypersaturation status.

In an embodiment of the present invention, a hypersaturation index iscalculated based on the reading of the R/IR ratio at the measurementsite. In an embodiment of the invention, a maximum hypersaturation indexthreshold is determined such that an alarm is triggered when thehypersaturation index reaches or exceeds the threshold. In anotherembodiment, an alarm is triggered when the hypersaturation index reachesor falls below its starting point when it was first calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings and following associated descriptions are provided toillustrate embodiments of the present disclosure and do not limit thescope of the claims. Corresponding numerals indicate correspondingparts, and the leading digit of each numbered item indicates the firstfigure in which an item is found.

FIG. 1 illustrates a perspective view of a patient monitoring system inaccordance with an embodiment of the disclosure.

FIG. 2 illustrates a block drawing of a patient monitoring system inaccordance with an embodiment of the disclosure.

FIG. 3A-3B illustrate graphs of SpO₂ versus PaO₂.

FIG. 3C illustrates a saturation calibration curve.

FIG. 3D-3E illustrate graphs of the difference between arterial andvenous saturation vs. perfusion index.

FIG. 3F illustrates the graph of the ratio of R/IR and PaO₂ vs. time.

FIG. 4 illustrates a graph of SpO₂ versus the R/IR ratio and ahypersaturation index versus the R/IR ratio.

FIG. 5 illustrates a flowchart depicting an embodiment of the invention.

FIG. 6 illustrates a flowchart depicting an embodiment of the invention.

FIG. 7 illustrates a visualization of an indication of hypersaturationaccording to an embodiment of the invention.

FIG. 8A-8B illustrate visualizations of indications of hypersaturationaccording to an embodiment of the invention.

FIGS. 9A and 9B illustrate a timer display illustrating when ahypersaturated patient will return to a normal saturation level.

FIGS. 10A and 10B illustrate an alternative embodiment of a timerdisplay.

FIG. 11 illustrates another alternative embodiment of a timer display.

DETAILED DESCRIPTION

Aspects of the disclosure will now be set forth in detail with respectto the figures and various embodiments. One of skill in the art willappreciate, however, that other embodiments and configurations of thedevices and methods disclosed herein will still fall within the scope ofthis disclosure even if not described in the same detail as some otherembodiments. Aspects of various embodiments discussed do not limit thescope of the disclosure herein, which is instead defined by the claimsfollowing this description.

Turning to FIG. 1, a patient monitoring system 100 is illustrated. Thepatient monitoring system 100 includes a patient monitor 102 attached toa sensor 106 by a cable 104. The sensor monitors various physiologicaldata of a patient and sends signals indicative of the parameters to thepatient monitor 102 for processing. The patient monitor 102 generallyincludes a display 108, control buttons 110, and a speaker 112 foraudible alerts. The display 108 is capable of displaying readings ofvarious monitored patient parameters, which may include numericalreadouts, graphical readouts, and the like. Display 108 may be a liquidcrystal display (LCD), a cathode ray tube (CRT), a plasma screen, aLight Emitting Diode (LED) screen, Organic Light Emitting Diode (OLED)screen, or any other suitable display. A patient monitoring system 102may monitor oxygen saturation (SpO2), hypersaturation, perfusion index(PI), pulse rate (PR), hemoglobin count, and/or other parameters.

FIG. 2 illustrates details of a patient monitoring system 100 in aschematic form. Typically a sensor 106 includes energy emitters 216located on one side of a patient monitoring site 218 and one or moredetectors 220 located generally opposite. The patient monitoring site218 is usually a patient's finger (as pictured), toe, ear lobe, or thelike. Energy emitters 216, such as LEDs, emit particular wavelengths ofenergy, typically red and infrared light signals, through the flesh of apatient at the monitoring site 218, which attenuates the energy. Thedetector(s) 220 then detect the attenuated energy and sendrepresentative signals to the patient monitor 102 for processing. Thepatient monitor 102 includes processing board 222 and a host instrument223. The processing board 222 includes a sensor interface 224, signalprocessor(s) 226, and an instrument manager 228.

The host instrument typically includes one or more displays 108, controlbuttons 110, a speaker 112 for audio messages, and a wireless signalbroadcaster 234. Control buttons 110 may comprise a keypad, a fullkeyboard, a track wheel, and the like. A patient monitor 102 can includebuttons, switches, toggles, check boxes, and the like implemented insoftware and actuated by a mouse, trackball, touch screen, or otherinput device.

The sensor interface 224 receives the signals from the sensor 106detector(s) 220 and passes the signals to the processor(s) 226 forprocessing into representations of physiological parameters. These arethen passed to the instrument manager 228, which may further process theparameters for display by the host instrument 223. The processor(s) 226may also communicate with a memory 230 located on the sensor 106; suchmemory typically contains information related to the properties of thesensor that may be useful in processing the signals, such as, forexample, emitter 216 energy wavelengths. The elements of processingboard 222 provide processing of the sensor 106 signals. Tracking medicalsignals is difficult because the signals may include various anomaliesthat do not reflect an actual changing patient parameter. Strictlydisplaying raw signals or even translations of raw signals could lead toinaccurate readings or unwarranted alarm states. The processing board222 processing generally helps to detect truly changing conditions fromlimited duration anomalies. The host instrument 223 then is able todisplay one or more physiological parameters according to instructionsfrom the instrument manager 228, and caregivers can be more confident inthe reliability of the readings.

Physiology Background

When oxygen molecules come into contact with blood, the majority of theoxygen molecules are bound to the hemoglobin in red-blood cells and asmall portion is dissolved directly in the blood plasma. Both of theseprocesses are driven by the partial pressure of oxygen. In the lung,oxygen diffuses across the alveolar membrane, and then the red cellmembrane in lung capillaries. When an oxygen molecule encounters amolecule of hemoglobin, it wedges itself between the iron atom and anitrogen atom attached to the globin chain. This helps to hold the hemegroup in place in the protein. One molecule of hemoglobin with its fourheme groups is capable of binding four molecules of diatomic oxygen, O₂.The pigment of the oxygen loaded heme group, which is calledoxyhemoglobin, is a brilliant red color. This is typically the color ofarterial blood. Pressure from dissolved oxygen in plasma and in thesurroundings in the red cell helps to keep the oxygen on its bindingsite.

As the blood circulates to the periphery, the small amount of plasmadissolved oxygen is consumed first by cells in organs and tissues, whichcauses a drop in the partial pressure of oxygen. This release inpressure makes available the much larger reservoir of heme-bound oxygenwhich begins a sequential unloading of its four oxygen molecules. At themost, under normal circumstances only 3 molecules of oxygen areunloaded. Partially or fully unloaded hemoglobin is calleddeoxyhemoglobin. It is a dark blue to purplish color. This is also thetypical color of venous blood.

There is a general relationship between the oxygen saturation in bloodand the partial pressure of oxygen. This nonlinear relation is describedby the oxygen dissociation curve as shown in FIG. 3A. FIG. 3Aillustrates a graph of SaO₂ versus the partial pressure of oxygendissolved in the arterial blood, PaO₂. As the partial pressure of oxygenin the arterial blood increases, the percentage of oxygen saturation ofthe hemoglobin will increase. After the SaO₂ level reaches 100%, thePaO₂ level continues to rise, but the SaO₂ level will not rise further.Thus, although it is possible to estimate PaO2 levels when SaO2 is below100%, as illustrated in FIG. 3A, after a certain point, very largechanges in the PaO₂ will produce little change in the SaO₂. A patientwhose physiology falls on the first part of the curve is commonlyreferred to as the Hypoxic. As can be seen from FIG. 3A, there is a highsensitivity around PaO₂=30 mmHg, i.e. the slope is large. A patientwhose physiology falls on the second part of the curve where SaO₂ beginsto level off is Normoxic. In the last portion of the curve, where SaO₂has reached 100%, a patient is considered Hyperoxic.

FIG. 3B illustrates a graph showing the potential shift in thedisassociation curve based on an individual patients response. Forexample a left shift may occur with decreased temperature, decreased1,3-diphosphoglycerate (2,30DPG), increased pH, or higher CO in theblood. As another example, a right shift will occur with reducedaffinity, increased temperature, increased 2,3-DPG and decreased pH.Thus, there is some uncertainty when determining PaO₂ based on the SaO₂measurement. This uncertainty can be reduced if the pH and temperatureare given as inputs to the device where an appropriate curve may beselected.

Oxygen Consumption

The following oxygen content equation relates the amount of oxygenpresent in the blood given certain hemoglobin concentration (tHb) andpartial pressure of oxygen (PaO₂)

ContO₂ (O₂ mL/dL)=tHb (gramHb/dL)·1.34 (ml O₂/gramHb)·SaO₂+0.0031 (mlO2/mmHg/dL)·PaO₂ (mmHg)  Eq. 1

Alternatively, the Oxygen Content can be measured directly using aMasimo Rainbow Pulse Oximeter available from Masimo Corporation ofIrvine, Ca.

Tissues need a requisite amount of O2 molecules for metabolism. Understeady state conditions the O2 consumption is fairly constant. In orderto quantify the relationship between oxygen transport and itsconsumption the Fick principle can be applied. The essence of the Fickprinciple is that blood flow to an organ can be calculated using amarker substance if the following information is known:

Amount of marker substance taken up by the organ per unit time

Concentration of marker substance in arterial blood supplying the organ

Concentration of marker substance in venous blood leaving the organ

In Fick's original method, the “organ” was the entire human body and themarker substance was oxygen.

This principle may be applied in different ways. For example, if theblood flow to an organ is known, together with the arterial and venousconcentrations of the marker substance, the uptake of marker substanceby the organ may then be calculated.

As discussed above, hemoglobin and plasma are the main oxygen vectors inthe blood. The oxygen content equation can be combined with the Fickprinciple to describe oxygen consumption and its relationship to bloodflow as shown below in Eq. 2.

OC=Ca·[1.34·tHb·(SaO2−SvO2)+0.0031·(PaO2−PvO2)]  Eq. 2

Where OC is Oxygen consumption (mL/min), Ca is Cardiac output (i.e.local blood flow at the test site (dL/min)), tHb is the Total hemoglobin(gram/dL), SaO2 is Arterial saturation fraction (0-1.0), SvO2 is Venoussaturation fraction (0-1.0), PaO2 is the Partial pressure of oxygen inthe arterial blood (mmHg), PvO2 is the Partial pressure of oxygen in thevenous blood (mmHg), 1.34 represents the HbO2 carrying capacity (mLO2/gram Hb), and 0.0031 represents O2 solubility coefficient in blood(mL O2/dL).

Noninvasive Oxygen Saturation Measurment

Pulse oximetry was invented by Dr. Ayogi in the 1972 as a technique tomeasure arterial oxygen saturation noninvasively. Dr. Ayogi was able toisolate the arterial pulse absorption from tissue, bone and cartilageabsorptions by looking at a signal synchronous with the heartbeatreflecting the local blood flow at the measurement site. This signal iscalled the photo-plethysmograph and it can be isolated by the use of ahigh-pass filter. By exploiting the predictable relationship betweenarterial oxygen saturation and light absorption through a vascular bed,the arterial blood oxygen saturation (SpaO₂) can be calculatednoninvasively. Note that the addition of a small p to SaO₂ to denotecalculation from an arterial pulse. It can be shown that the use of twodistinct light sources, Red (R)=660 nm and Infrared (IR)=910 nm, a pulseoximeter can calculate the oxygen saturation noninvasively by relating aratio=R (AC/DC)/IR (AC/DC) to the hemoglobin oxygen saturation through atypical pulse oximeter calibration curve shown in FIG. 3C. We will referto this ratio as (R/IR) ratio.

Modifying Eq. 2, if (SaO₂−SvO₂) is replaced with ΔSat, (PaO₂−PVO₂)replaced with ΔP, Ca replaced with the local blood flow (BF), the oxygenconsumption is set to a constant and the equation is solved for BF, Eq.3 results:

BF=Const/[1.34·tHb·ΔSat+0.0031·ΔP]  Eq. 3

Eq. 3 shows an inverse relationship between blood flow and thearterio-venous saturation difference, ΔSat, as well as arterio-venous O₂partial pressure difference (ΔP). At normal inspired oxygen levels, themajority of the oxygen is supplied by the hemoglobin. But when theconcentration of inspired oxygen is raised, its partial pressureincreases, hence ΔP, and more oxygen is delivered to the tissue throughthe O₂ dissolved in the plasma. Based on Eq. 3, if we consider a digitwhere a pulse oximeter probe is placed, the increase of inspired oxygenpartial pressure will lead to a decrease in the arterio-venous ΔSat.This is true whenever the oxygen consumption is relatively constant.

In a vascular bed the arterial vasculature is coupled mechanically tothe venous vasculature through the tissues. Although this coupling issmall, the optical arterial pulse, e.g. photo-plethysmograph, hasinvariably a small venous component. This component is not fixed acrosssubjects but its average is indirectly calibrated for in the saturationcalibration curve. Its effect on the arterial pulse is proportional tothe coupling size as well as the difference between the arterial andvenous saturations at the site. Let us consider a typical subject atroom-air saturation of 98%. Looking at the saturation calibration curveof FIG. 3C, a (R/IR) ratio of 0.53 corresponds to 98% saturation. If theinspired oxygen concentration is increased beyond the normal O2=21%, the(R/IR) ratio continues to drop below 0.53. An example is shown in FIG.3F where the ratio starts at 0.43 and goes down to 0.43. It can evenreach a level as low as 0.3 on some subjects at an inspired O2=100%.

This behavior may be explained by the reduction in the optical effect ofvenous coupling as the delta saturation between the arterial and thevenous is reduced due to the increase in availability of plasma oxygen.Under this condition, the venous blood will look, optically, a lot likethe arterial blood. Hence, the size of the Red photo-plethysmographsignal will shrink with respect to the IR indicating a shrinking ΔSat,i.e. higher venous saturation. In 1995, Masimo Corporation (Masimo)introduced a new technique for calculation the venous oxygen saturation(SpvO₂) by introducing an artificial pulse into the digit (see, e.g.,U.S. Pat. No. 5,638,816, incorporated herein by reference). By using apulse oximeter with a probe and a subject's digit, a continuous measureof SpaO₂ and SpvO₂ can be calculated. The blood perfusion index (PI) isused as a proxy for the blood flow to the digit. FIG. 3D depicts such aninverse relationship between blood flow (BF) and arterio-venoussaturation ΔSat.

FIG. 3E depicts the effect of increasing the inspired O₂ concentrationon the calculated ΔSat. As expected there is a commensurate reduction inthe ΔSat with the increase of oxygen concentration. The arterio-venousΔSat will continue to decrease if the oxygen pressure is increasedbeyond atmospheric pressure. However, a point of diminishing return willbe reached where no more change is possible. At that point the R/IRratio will stop changing as shown in FIG. 3F. The increase in PaO₂ canbe indirectly monitored beyond the normal 100 mmHg by looking at theeffects of shrinking ΔSat. This cannot be done by looking at the SaO₂ asit will plateau at 100%.

FIG. 4 illustrates a graph of SpO₂ saturation percentage 400 versus theR/IR ratio 401 according to an embodiment of the invention. In theillustrated example, the R/IR ratio is at 0.5 when the SpO₂ maxes out at100%. While the SpO₂ level will max out at 100% saturation, the R/IRratio continues to drop when more oxygen is dissolved in the blood. Anembodiment of the invention calls for calculating a hypersaturationindex 402 based on the R/IR ratio after the point 403 where the R/IRratio translates to a SpO₂ level of 100% saturation. Thishypersaturation index 402 assists medical practitioners in exercisingtheir judgment in ensuring that the patient's blood is not toooversaturated with oxygen. In another embodiment, the hypersaturationindex is calculated in response to a user signal, i.e., not necessarilyat the point where the SpO₂ level is at 100% saturation.

Determining a level of hypersaturation is particularly important in avariety of patient types. For example, patients on supplemental O₂titration are at risk of complications caused by hypersaturation.Patients on a ventilator or where FiO2 therapy is given to the patientare also at risk. Further, closed loop positive pressure O₂ delivery orFiO₂ delivery devices also place a patient at risk of hypersaturation.This may include, for example, CPAP machines or those sufferingobstructive sleep apnea.

In an embodiment of the invention, the patient's oxygen saturation levelSpO₂ is determined and monitored. When the saturation level reaches100%, an indication of rising oxygen levels, such as a hypersaturationindex, is calculated. The indication of rising oxygen levels may also bedisplayed on an output device such as the display 108 in FIG. 1. FIG. 5is a flowchart that illustrates this embodiment of the invention. Inthis embodiment, the patient's blood oxygen saturation level SpO₂ isdetermined at step 500. If the blood oxygen saturation level maxes outat 100% at step 520, an indication of hypersaturation is calculated atstep 530 and displayed at step 540.

In another embodiment of the invention, illustrated in FIG. 6, thepatient's oxygen saturation level SpO₂ is determined and stored at step620 in response to a signal from the user at step 610. The signaltypically indicates that a medical procedure is about to begin. A basehypersaturation index value is then calculated at step 630 based on thestored oxygen saturation level and the R/IR ratio. The hypersaturationindex is then monitored at step 640 as the patient's oxygen saturationlevel changes. Next, an alarm trigger is generated at step 660 when thehypersaturation index value is less than or equal to the basehypersaturation index value as determined in step 650. Finally, an alarmis activated at step 670 in response to the alarm trigger.

In an alternative embodiment, the oximeter monitors a patient andautomatically determines a baseline oxygen saturation level and/orbaseline ratio from stable measurements taken when the oximeter firstbegins measurements. The oximeter can indicate that a baselinemeasurement has been determined or can indicate that it is unable todetermine a baseline measurement if stable measurements cannot beobtained. Once a baseline measurement is obtained, the oximeter willmonitor the patient for an inflection point in the saturation and ratiocalculations. If the oximeter finds an inflection point where thepatient's oxygen saturation begins to rise and/or ratios begin to fall,it will determine that oxygen is being administered to the patient. Inthis way, a caregiver is not required to push a button or otherwiseindicate the start of a procedure or the start oxygen administration.Along the same lines, once a patient is hypersaturated, the oximeterwill monitor the saturation level and/or ratio calculations of thepatient for an inflection point indicating that oxygen is no longerbeing administered to the patient. Again the oximeter will alarm whenthe oxygen saturation values and/or ratios return to their normalbaseline levels.

In yet another embodiment of the invention, a maximum hypersaturationindex value is also calculated and stored in response to a user signal.In this embodiment, an alarm trigger is generated when the monitoredhypersaturation index value is more than or equal to the maximumhypersaturation index value.

In an alternative embodiment, a visual oxygen hypersaturation alarm isactivated. The oxygen hypersaturation alarm may include text thatindicates that the oxygen hypersaturation index has dropped below thebase hypersaturation index value. In another embodiment, the alarm mayinclude text that indicates that the oxygen hypersaturation index hasexceeded a threshold value. The visual oxygen hypersaturation alarm maybe accompanied or replaced by an audio alarm in certain embodiments.

FIG. 7 illustrates an example of a visualization of an indication ofhypersaturation according to an embodiment of the invention. Thisvisualization can be displayed on a display, such as the display 108 inFIG. 1. In the illustrated embodiment, the indicator is displayed as aspeedometer-type visualization. The display includes a pointer 700 thatpoints to the current value of the hypersaturation indicator. The value,for example, can be on a scale of 0-100 or 0-10 to differentiate fromoxygen saturation. In one embodiment, the spectrum of possible levelsmay be indicated by various shades or colors. For example, the low rangeof values may be indicated by an area 701 that is green in color, themedium range in values may be indicated by an area 702 that is orange incolor, and the high range in values may be indicated by an area 703 thatis red in color.

FIG. 8A illustrates another example of a visualization of an indicationof hypersaturation according to an embodiment of the invention. Thisvisualization can also be displayed on a display, such as the display108 in FIG. 1. In the illustrated embodiment, the hypersaturationindicator is displayed as a bar 800. In one embodiment, the size of thearea of the bar that is shaded or colored depends on the value of thehypersaturation indicator. For example, a low value may be representedby a small shaded area below the “L” level 801. A medium value may berepresented by a larger shaded area that remains below the “M” level802. Finally, a high value may be represented by an even larger shadedarea that can cover the entirety of the bar up to the “H” level 803.

FIG. 8B illustrates yet another example of a visualization of anindication of hypersaturation. The displayed graph 820 illustrateshypersaturation on a scale of 0-100%. The line 821 illustrates anestimated hypersaturation value. The shaded area 823 illustrates thevariability of the hypersaturation index. In other words, each patient'sphysiology is different and depending patient, their hypersaturation mynot exactly follow the population average. This is explained in moredetail, for example, with respect to FIG. 3B. Thus, the shaded area 823provides an indication of the uncertainty in the estimate 821. Thisprovides a care provider with a better indication of the actualhypersaturation that the patient is experiencing. In the embodiment ofFIG. 8B, 0% represents no detectable oxygen reserve, or no indication ofhypersaturation. 100% indicates a maximum detectable reserve or amaximum hypersaturation.

FIG. 9A illustrates an embodiment of a hypersaturation timer 900. Ahypersaturation timer 900 is useful, for example, during procedures suchas a patient intubation when the patient is forced to stop breathing.The timer provides an indication of the amount of time a care giver hasbefore the patient returns from a hypersaturated state to a baselinesaturation state. The timer includes a countdown indications 901-905. Inthe embodiment of FIG. 9A, the countdown begins at about 60 seconds andcounts down to zero. When the counter is initially started, the amountof time a patient will take to return to a baseline saturation state isrelatively difficult to determine. Thus, the timer 900 provides a rangeof time left which is illustrated by shaded area 907. The shaded areamoves clockwise around the timer indicating a range of time left beforethe patient reaches a baseline state. As time goes by, the amount oftime a patient will take to return to a baseline saturation statebecomes more predictable based on how quickly the ratios change. Thus,as illustrated in FIG. 9B, the range indicated by the shaded area 910becomes smaller.

FIG. 10 illustrates another embodiment of a timer 1000. Similar to FIGS.9A and B, timer 1000 has a count-down range 1002 that decreases as timeexpires and the time in which a patient returns to their base linesaturation becomes more certain.

In another embodiment not shown, a simple digital count-down clock couldalso be used to indicate the amount of time left for a hypersaturationpatient to return to their baseline saturation level. The count-downclock can indicate a range or it can simple indicate a number and speedup or slow down based on the rate of return experienced by the patient.

FIG. 11 illustrates an embodiment count down display of an oxygenreserve, or the time left for a hypersaturation patient to return tobaseline saturation. Put in other terms, the time in seconds startsincreasing from zero as a subject transitions from normoxia tohyperoxia. The display then decreases when the subject transitions fromthe Hyperoxic state to the Normoxic state. The display of FIG. 11includes an arc indicator, for example, arc indicators 1101, 1102, and1103. The indicators are arced in order to show the uncertainty range inthe time left in the display. Although the arcs 1101, 1102, and 1103 areall illustrated on the display for illustration and explanationpurposes, it is to be understood that during measurement, only a singlearc is displayed which according to the relative time

Although the foregoing has been described in terms of certain specificembodiments, other embodiments will be apparent to those of ordinaryskill in the art from the disclosure herein. Moreover, the describedembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of other formswithout departing from the spirit thereof. Accordingly, othercombinations, omissions, substitutions, and modifications will beapparent to the skilled artisan in view of the disclosure herein. Thus,the present disclosure is not limited by the disclosed embodiments, butis defined by reference to the appended claims. The accompanying claimsand their equivalents are intended to cover forms or modifications aswould fall within the scope and spirit of the disclosure.

1. (canceled)
 2. A pulse oximeter configured to measure an indication of oxygen saturation of a patient, the pulse oximeter comprising: one or more light emitters configured to emit light of at least two wavelengths of light into tissue of a patient; one or more detectors configured to output a signal responsive to detected light after attenuation by the tissue of the patient; one or more signal processors configured to receive the signal and determine at least one ratio from the signal, the at least one ratio comparing detected light of one of the at least two wavelengths to detected light of another of the at least two wavelengths, the one or more signal processors further configured to map the at least one ratio to either an oxygen saturation value or a hypersaturation value, wherein the ratio is mapped to a hypersaturation value if the ratio is below a first threshold and the ratio is mapped to an oxygen saturation value if the ratio is above the first threshold; displaying either the oxygen saturation value or the hypersaturation value.
 3. The pulse oximeter of claim 2, wherein the first threshold is set at a ratio value that maps to a 100% oxygen saturation value.
 4. The pulse oximeter of claim 2, wherein the ratio is mapped to an oxygen saturation value if the ratio indicates hemoglobin carriers are less than fully saturated, and wherein the ratio is mapped to a hypersaturation value if the ratio indicates the hemoglobin carriers are fully saturated and additional oxygen is dissolved in the blood stream.
 5. The pulse oximeter of claim 2, wherein the oxygen saturation value ranges from 0-100 and wherein the hypersaturation value ranges from 1-10.
 6. The pulse oximeter of claim 2, wherein the oxygen saturation value is displayed separately from the hypersaturation value.
 7. A method of measuring a hypersaturation level of a patient, the method comprising: emitting light of at least two wavelengths from one or more light emitters; detecting the emitted light after attenuation by tissue of a patient by a light detector; providing a signal representative of the detected emitted light to a signal processor; processing the signal to determine an indication of a hypersaturation state of a patient, the hypersaturation state indicating the presence of more oxygen in blood of the patient than a 100% oxygen saturation level; displaying the indication of the hypersaturation state.
 8. The method of claim 7, wherein the indication of the hypersaturation state is determined based on a calculation of a first of the at least two wavelengths to a second of the at least two wavelengths.
 9. The method of claim 7, wherein the indication of the hypersaturation state is determined using the same equation used to determine oxygen saturation measurements at or below 100%.
 10. The method of claim 7, wherein the indication of the hypersaturation state is a separately displayed index from oxygen saturation.
 11. The method of claim 7, wherein the indication of the hypersaturation state is displayed with oxygen saturation.
 12. A pulse oximeter configured to measure an indication of oxygen saturation of a patient, the pulse oximeter comprising: one or more light emitters configured to emit light of at least two wavelengths of light into tissue of a patient; one or more detectors configured to output a signal responsive to detected light after attenuation by the tissue of the patient; one or more signal processor configured to determine a blood oxygen saturation level of the patient, wherein if the blood oxygen saturation level is at 100%, the one or more signal processors configured to calculate an indication of hypersaturation.
 13. The method of claim 12, wherein the indication comprises an index.
 14. The method of claim 12, further comprising a display configured to display one or both of the oxygen saturation level or the indication of hypersaturation.
 15. The method of claim 12, wherein the indication comprises a measure of oxygen.
 16. The method of claim 15, wherein the measure of oxygen comprises a measure of oxygen dissolved in the blood.
 17. A pulse oximeter configured to measure an indication of oxygen saturation of a patient, the pulse oximeter comprising: one or more light emitters configured to emit light of at least two wavelengths of light into tissue of a patient; one or more detectors configured to output a signal responsive to detected light after attenuation by the tissue of the patient; one or more signal processor configured to determine an indication of hypersaturation of the patient and display the indication.
 18. The method of claim 17, wherein the indication comprises an index.
 19. The method of claim 17, wherein the indication comprises a measure of oxygen.
 20. The method of claim 19, wherein the measure of oxygen comprises a measure of oxygen dissolved in the blood. 